Art of spray coating of tubes



June 4, 1957 H. MARANTz 2,794,443

ART OF SPRAY COATING OF TUBES I.

Original Filed April 9', 1949 2 Sheets-Sheet l INTERNAL PA\NT|NG UN \T WSINVHQBW GBSdEALLISOd June 4, 1957 l. H. MARAN-rz 2,794,448

ART GIP/SPRAY COATING OF TUBES Original Filed April 9, -1949 2 Sheets-Sheet 2 35 rl-q'' ATTORNEYS ART F SPRAY COATING 0F TUBES Israel H. Marantz, Forest Hills, N. Y., assignor to Columbia Cable & Electric Corporation, a corporation of New York Original application April 9, 1949, Serial No. 86,532, now Patent No. 2,683,438, dated July 13, 1954. Divided and this application January 18, 1952, Serial No. 267,156

2 Claims. (Cl. 13S-68) Unless metal tubes such as the type used in electrical installations, as they come from the forming mill, are lirst cleaned by removing the adherent lubricating grease and oils, scales, rust and grit, from the outer and bore surfaces of the tube, and unless the tubes are dried before coating with the required corrosion resistant metal, plastic or paint, such coatings may not adhere adequately and unless the cleaning and coating processes can be performed at a relatively high rate of speed Without manual labor or waste of material, the cost of manufacture of the finished product may be excessive and not justified by the price at which such tubes may be sold.

Where high temperature for long periods is resorted to for application of the metal outer coating, such as where the hot dip galvanizing or Sherardizing processes are used, the outer surface of the tube may harden unduly and tend to crack or split, upon the bending frequently required in installation and the tube may warp due -to the application of such heat which would require an additional straightening process. Where such two processes Vare used to apply a zinc coating to the tubes, a non-ferrous metal coating such as an iron zinc alloy coating will be alloyed with the tube, and as such alloy is less ductile and pliable than the tube itself, it will tend to crack or peel oi especially in bending.

While a pure non-ferrous metal coating may be applied by electroplating, the cost of the equipment for such process, the installation cost thereof, the cost of maintenance and the power costs are high while the operation is relatively slow with consequent relatively low output thereby resulting in an inefcient operation.

Where it is desired to provide a relatively thick zinc coating on the metal tubing, if the Sherardising process is used, as the coating applied by such process becomes more and more brittle as the thickness of the coating is increased, such coating is likely to crack and peel upon bending of the tube.

' If it is desired to apply such thick coating by electroplating, the operation is extremely time-consuming and costly with resultant high cost of the nished product.

Where the metal coated surface of the tube is relatively smooth, it slips too readily in the hand and affords insulicient friction for application of the eld bending tool. Moreover, an outer coaitng whichmay be of metal, plastic or Ypaint will have inadequate adhesion upon such smooth metal coating and will readily crack or peel ott suchsmooth tube, especially when bent.

Where the metal conduit has a threaded end, if the coating should be applied in such a manner as to till the threads, the latter would have to be recut and a new coating applied to such recut threads. Such procedure is time-'consuming and costly.

lt is accordingly among the objects of the invention to provide a method expeditiously and reliably to convert the steel tube as originally formed with lubricating grease, oil,V scale, Vrust and grit adhering thereto into a finished, interiorly and exteriorly degreased and cleaned States Patentand exteriorly roughened and metal sprayed and interiorly painted tube.

Another object is to provide a method for metal coating the outer surface of metal tubes with a layer of any desired thickness without the use of high temperature for long periods of time and with consequent avoidance of lthe objections above pointed out, to the surface hardening of the tube under heat; which coat is not of alloy character and avoids the objections of peeling or cracking oil' especially when the -tube is bent and which coating is not so smooth that a coating of metal, plastic or paint thereon will tend to peel or crack off therefrom especially in bending the tube.

Another object is to provide a method expeditiously and reliably to convert a smooth steel tube having a threaded end, into a -linished interiorly and exteriorly degreased and cleaned and eXteriorly roughened and metal sprayed tube in which the threaded end will be coated and does not require rethreading.

Another object is to provide a metal tube having a non-ferrous metal coating on the entire outer roughened surface thereof having a substantially porous mat finish, which coating is of ductility and pliability no less than that of the metal tube covered thereby so that the tube may be bent without cracking or peeling olf of the coating thereon. v

Another object is to provide a metal tube having a non-ferrous metal coating on the entire roughened outer surface thereof to which a second coating will securely bond so that the tube may be bent without cracking or peeling ofi of the coating thereon.

This application is a division of co-pending application Serial No. 86,532, tiled April 9, 1949, now Patent No. 2,683,438, July 13, 1954.v

ln the accompanying drawings in which are shown one or more of various possible embodiments of the several features of the invention,

Fig. l is 4a diagrammatic view of one type of equipment, with parts broken away, for practicing the invention, and

Figs. 2, 3 and 4 are longitudinal sectional views of coated tubes according to various embodiments of the invention.

Although the invention may be practiced by the use of any one of a number of types of equipment, it is preferred to utilize the equipment shown in co-pending patent application, Serial No. 86,532, led April 9, 1949.

Referring now to the drawings, as diagrammatically shown in Fig. l, the installation desirably comprises a plurality of operating units which successively act upon the tubes to form the completed product.

These operating units may include a cleaning unit 11 for removing lubricating grease, oils, scales, rust or grit from the surface of the tube, a roughening unit 12 for roughening and cleaning the outer surface of the tube, a blowout unit 13 for removing grit or dirt from the bore of the tube, a metal spraying unit 14 for applying a basic metal coating to the exterior of the tube, a second spraying unit 15 for applying a second coating and a painting unit 16 for coating the interior of the tube, suitable mechanism such as the type shown in such co-pending patent application above described, being provided at each of said units to perform the required operation. If desired,` a burnishing unit 17 may be interposed between the second spray unit 15 and the painting unit 16 slightly to smoothen the pipe in the event a metal coating is appliedto the basic coating.

ln the operation of the installation shown in Fig. 1, de-

grease, oil, scale, rust or grit and discharged in spaced Patented June 4, 195,7

relation upon a conveyor system 19 which may comprise a plurality of skew rollers which function in conventional manner simultaneously to rotate the tubes while advancing them lengthwisel through the roughening unit 12,; Although the roughening unit 12 may be of anyV suitable type, it desirably comprises a centrifugal rotor 21 supplied with abrasive material from a hopper 22 and which, upon rotation,.hur1s such abrasive material against the tubes to clean off carbon, rust and scale deposits therefrom and roughens the outer surface of such tubes. The roughened tubes are thereupon advanced in sequence by said conveyor system 19 to a blowout unit 13 at which thetubes Y are removed from the conveyor system 19 as in the manner described in saidjpatent application above describe and presented to an air nozzle 23` which discharges a jet of air therethrough and thereupon replaces such tubes uponV the conveyonsystem 19 to be. advanced thereby to the rst metal spraying unity 14.

In lorder that the metal spray be. equally distributed in a uniform layer over-the entire outer surface ofthe tubes andthat no area of the tube is exposed to the heated metal spray for any excessive length of time, it is desirable that the tubes be simultaneously advanced and rotated at uniform speed as they are moved through the spray unit. To this end, for the metal spraying operation, a feed mechanism 25, which may be of the typeshown in said patent application, positively grips the tubes and simultaneously rotates and advances the latter ata controlled rate of speed past metal spray means. Such means may comprise guns 26 of the Schori type which deposit a uniform coating of any desired thickness onthe tubes, such coating preferably being of some non-ferrous metal such as zinc which has an anodic protection for steel, another coating metal well known to those skilled in the art to be equivalent to zinc in its anodic protection for steel, being aluminum. The sprayed tubes may then be conveyed to another spray unit 15 which rnay deposit another metal. coating7 such as zinc, a plastic coating or apaint coating on the basic metal coating. The sprayed tubes are thereupon desirably conveyed to a painting unit 16 preferably being presented thereto at an incline, and the painting unit injects a quantity of paint into the bores of theV tubes, the latter thereupon being rotated to distribute such paint upon the entire inner surface thereof. Itis of course to be understood that the burnishing means 17 are only provided where metal coatings are applied, slightly to smooth the roughlened'V outer surface. of the tube. v

With the method herein described, metal tubes may be roughened and cleaned, particles removed from the bore thereof, a metal coating of uniform thickness sprayed on the exterior of the tubes and a second coating of metal, plastic or paint may be sprayed on the basic coating and the tube may be painted on the interior thereof and dried all in a speedy, continuous operation without manual handling. As the heated metal particles from the spray guns are sprayed on the tube while it is being rapidly rotated and advanced, the particles will congeal rapidly and althoughk the tube will become suiliciently heated to aid in the drying of the paint subsequently injected therein, no portion of the tube will be exposed to high temperature for any considerable period of time.

The resultant product shown in Fig. 2 thus has a roughened outer coatingy ofV pure non-ferrous metal 31, illustratively of Zinc formed from the discrete particles sprayed thereon, which congeal to completely cover the outer surface thereof with a substantially porous mat nish and forming substantially an integral part ofthe metal' tube 18, and ininterior coating 32 of paint. In addition, as shown in Fig. 2, a second zinc coating 33 may be bonded to the basic coating 31 the porosity of the latter permitting the second coating to penetrate thereinto for effective bonding action. Instead of such second coating being of zinc as shown in Fig. 2, it may be of plastic 34 as shown in Fig., 3 or of paint 35 'as shown in Fig. 4. Inl all casesthe coatings securely bond to the basic substantially po rous metal coating 31. As the coatings are ductile and pliable, the tubes may be bent without cracking of such coatings which might cause rusting of the metal tube therebeneath.

The method above described will also permit the coating of tubes having threaded ends 36 without filling up such threads, which would require recutting. This is by virtue of the fact that thetube is continuously advancing during the spraying operation and insumcient time will elapse to permit lling of the threads.

By congealing is meant the conversion to the firm or relatively rigid non-flowable condition of the particles which emerge from the spray guns in owable or plastic state.

Although the method above described has been shown as applied to relatively thin walled metal tubing, it isof course to be understood that it could just as readily'be applied to metal tubing having regular pipe Wall thickness.

As many changes could be made in the above method and article, and many apparently widely different embodiments of this invention could be made without departing fromV the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

' Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

l. The method of coatinga metaltube which comprises the successive steps of cleaning and roughening the tube, simultaneously and continuously rotatingthe tube in one direction and advancing the latter past continuously operating metal spray means for discharge of heated metal particles on the cleaned and roughened outer surface of the tube and while the tube isV still inheated condition as a result of such metal spraying, injecting paint into the bore of the tube and rotating the tube for distribution of such paint overy the entire inner surface thereof, the residual heat in the metal tube. effecting rapid setting and drying of such paint to insure that'the entire innerv surface of the tube will be uniformly coated with such paint.

2. As an article. of manufacture, a steel conduit having Y acleaned, roughened outer surface having a hot-sprayed coating of all-metallic non-ferrousparticles thereon of the type aifording anodic protection for steel andcompletely covering and in contact with said cleaned, roughened outer surface. to` provide a substantially porous mat finish thereon, said hot sprayed coating metal being selected from the groupv consisting of zinc and aluminum, whereby said non-ferrous metal coating constitutes substantially an integral part of the conduit and is of ductility and pliability no less than that of the conduit which it covers so that said conduit may be bentwithout cracking of the coating thereon or separation. of the coating therefrom.

References Cited in the le of this patent UNITED STATESVPATENTS 1,947,493 Rose et al'. Feb. 20, 1934 1,978,415 Collins Oct. 30, 1934 1,997,761 Bailey et al Apr. 16, 1935 2,066,592 Wadsworth Ian. 5, 1937 2,084,209 Mclroy June 15, 1937 2,228,102 Yeager Jan. 7, 1941 2,320,328 Meduna May 25, 1943 2,373,638 Perkins Apr. 10, 1945 2,427,350 Carpenter etal'. Sept. 16, 1947 2,447,420 Moore .Aug. 17, 1948 2,470,689 Crampton May 17, 1949 FOREIGN PATENTS 113,891 Australia Sept. 17, 194'1 

